This invention relates to a novel process for the preparation of acrylate esters. More specifically, the invention relates to a vapor phase carbonylation of haloalkenes using heterogeneous catalysts to prepare acrylate esters.
One such acrylate ester is methylmethacrylate which is prepared commercially from acetone which is treated with HCN to give 2-cyano-2-propanol which is then treated with 98 percent sulfuric acid to give a salt of propene-2-amide and sulfuric acid. The salt is then reacted with methanol to prepare methylmethacrylate and ammonium sulfate. This process requires a large purification scheme and the use of sulfuric acid and hydrogen cyanide.
Heck, U.S. Pat. No. 3,988,358, discloses the preparation of alpha-unsaturated carboxylic esters have been prepared from olefinic halides, wherein the olefinic halides are contacted with carbon monoxide and an alcohol, phenol or polyglycol in the presence of an organic halide of a Group VIII metal catalyst. The Group VIII metal catalyst is added as finely divided palladium metal wherein the organic halide is an organic iodide or in the salt form to the reaction solution. It is further taught that the catalytic species is RPdL.sub.2 X wherein R is aryl, heterocyclic, vinylic, ethynylic or benzylic or substituted derivatives thereof; L is a coordinating group such as triphenyl phosphine; X is Cl, Br or I; and n is 2, 3 or 4. It is further taught that the use of tertiary amines is usually necessary to make the reaction catalytic in palladium. This homogeneous process has a significant disadvantage in that the products are very difficult to recover, furthermore, recovery of the catalyst is also difficult.
Closson et al., U.S. Pat. No. 3,457,299, disclose a process for preparing unsaturated carboxylic acids by reacting a halogenated olefin and carbon monoxide, using as a catalyst rhodium, iridium, platinum, palladium, osmium, or ruthenium metal, or mixtures thereof. The halogenated olefin (1) must be stable to the reaction conditions, (2) must have the basic structure ##STR1## and (3) cannot be substituted with a group which retards or hinders the carbonylation. Preferred halogenated olefins are those with the structure ##STR2## It is taught that the by-product is ##STR3## The reaction conditions used include pressures of 50 psi to 10,000 psi, with a highly preferred range of 2,000 psi to 5,000 psi, and temperatures from 250.degree. C. to the decomposition temperature of the halogenated olefin. This process suffers from significant problems, specifically the catalyst demonstrates low conversions and relatively short lifetimes under the reaction conditions taught.
Scheben et al., U.S. Pat. No. 3,626,005, disclose the formation of unsaturated acid halides by the reaction of a haloalkene with carbon monoxide. It is further taught that alcohols can be used as diluents. The acid halide is recovered as the corresponding ester when alcohols are used as diluents. Alternatively, the recovered acid halide can be converted to an ester by contacting it with an alcohol. This process suffers from the problem that the productivity of the catalysts is low.
Scheben et al., Catalysis in Organic Synthesis, (5th Conf.), p. 181 (1975), teach that the reaction of 2-chloropropene with carbon monoxide in the presence of a heterogeneous palladium on alumina catalyst results in the transposition of the chlorine atom to the saturated carbon atom, and the formation of 3-butenoyl chloride as the product. It is further taught that 2-chloropropene isomerizes to allyl chloride in the presence of palladium catalysts.
The hereinbefore described carbonylation processes suffer from several problems. First, the homogeneous process creates significant problems in the recovery of both the catalyst and the product. The catalyst lifetimes in the processes described hereinbefore are very short. These processes demonstrate a low selectivity for the desired carboxylic acid esters. Furthermore, the productivity of the catalysts is too low to justify commercialization.
What is needed is a heterogeneous catalyst for the carbonylation of haloalkenes to prepare carboxylic acid esters wherein the catalyst demonstrates extended lifetimes, with good selectivities towards the desired carboxylic acid esters and the catalyst demonstrates a high productivity.